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<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
     var sum = 0; // 累加器
        for (var i = 1; i <= 100; i++) {
            sum = sum + i;
            // debugger;
        }
        // 0+1+2+3+4+..+100 
        console.log(sum)

        function add(a,b){
          return a + b
          // console.log(a + b)
        }

        console.log(add(20,3))

        var arr = [1,2,3,4,5]
        arr.forEach(function(item,index){
          console.log(item,index);
        })
  </script>
</body>
</html>